Field of the Invention
The present invention relates to a method of and a system for monitoring input packet rate in a packet network and in particular to a packet rate monitoring method and system for detecting the excessive transmitted packets (violation packets) which violate a contract, i.e., a preliminary agreement made between a subscriber and a network provider (communication network control system) for a communication network using Asynchronous Transfer Mode (ATM).
Description of the Related Art
ATM networks which have been studied in various research institutes as next generation prominent communication systems enable communication of information such as audio, video and data by various media having different transmission rates in the same network by transmitting information in packets having fixed lengths (hereinafter referred to as "cell") at a high rate.
Generally, the capacity of communication provided by a network has a limitation. Accordingly, a network control system (hereinafter referred as a network provider) has the subscriber declare the communication condition such as transmission rate, etc. when the system accepts a call request from the subscriber (terminal unit) and permits the call request when it determines that the passing cell rate will not exceed the communication capacity in the network if the call request is permitted.
However, since the utilization efficiency of resources is enhanced by commonly using resources such as communication nodes and links by a plurality of subscribers, the rate of cells passing through the network may exceed the communication capacity of the network under a circumstance if any of the subscribers transmit the excessive cells which violate his own declared parameter. For example, phenomena such as missing of a part of information or extension of delay time of transmission or switching of information may occur. This will deteriorate the communication quality of the other subscribers which do not violate their own declared parameters.
Therefore, the ATM network requires cell rate monitoring means which detects cells which are transmitted by a subscriber who violates the declared parameter (hereinafter referred to as "violation cells") for regulating the violation cells flowing into the network.
Such a technique for detecting violation packets in a packet communication network has been proposed by, for example, JA-P-A 2-220531 entitled "Call connection control system and rate monitoring system". In this proposed technique, the number of arrival packets within unit time .DELTA.t is counted and stored for each terminal every time the packets arrive at the network from each terminal. If the count exceeds the parameter (the maximum number m of the transmitted packets in unit time .DELTA.t) which the terminal declared on call request, the system determines that the transmission violets the contract and immediately regulates the arrival packets transmitted from the violation terminal.
In a ATM network, a multiplexer for accommodating a plurality of terminal units may be provided, for example, between the terminal units and a network terminating circuit which is an entrance of the network. In this case, the number of input lines of the multiplexer, the number of output lines of the multiplexer, the transmission speed on the input lines and the transmission speed on the output lines are represented as n (n=1,2,3, . . .), 1, v and kv, respectively. If cells from (k+1) or more terminal units simultaneously arrive at the multiplexer, the number of input cells exceeds the processing capacity of the multiplexer. Some of the arrival cells temporarily stay in a buffer memory in the multiplexer, resulting in delay of cells. This delay time is proportional to the number of cells which simultaneously arrive at the multiplexer.
Since the number of cells which simultaneously arrive at a multiplexer randomly changes, and the delay time correspondingly changes, the intervals between cells which have passed through the multiplexer are different from those between cells which pass through the terminal unit. In other words, a change in cell interval after passing through the multiplexer means a change in the number of arrival cells in unit time .DELTA.t. The change in cell interval depends upon the external condition in which the multiplexer is used. For example, the higher the utilization of the output lines of the multiplexer becomes, or the larger the number of terminal units to be multiplexed in the multiplexer becomes, the larger the change in cell interval becomes.
In accordance with the prior art packet rate monitoring method, every time when cells arrive at a network terminating unit, the number of arrival cells transmitted from a terminal in unit time .DELTA.t is counted and the arrival cells are regulated as violation cells at the time when the count exceeds the declared parameter (maximum rate m). However, if the above mentioned multiplexer is interposed between terminal units and a network terminating unit which monitors the cell rate and if the intervals between cells inputted to the network terminating unit becomes shorter due to changes in external condition, the number of arrival cells in unit time .DELTA.t which is monitored by a monitor is larger than the number of cells actually transmitted from the terminal unit. Accordingly, even if the terminal unit keep the declared parameter, the network terminating unit may erroneously determine that the terminal violates the declared parameter. Conversely, when the cell interval becomes longer by the influence of the change in cell interval, the number of cells which arrive at the network terminating unit in unit time .DELTA.t decreases. Even if the terminal unit violates the declared parameter, the network terminating unit may miss the violation.
It is necessary to control the detection error rate relating to the above mentioned declared parameter violation to sufficiently low in order to assure excellent communication quality. However, since factors which individual terminal units are not responsible for are not considered in accordance with the prior art method, an appropriate cell rate control can not be achieved.